A leading cause of death in the United States today is coronary artery disease, in which atherosclerotic plaque causes blockages in the coronary arteries, resulting in ischemia of the heart (i.e., inadequate blood flow to the myocardium). The disease manifests itself as chest pain or angina. In 1996, approximately 7 million people suffered from angina in the United States.
Coronary artery bypass grafting (CABG), in which the patient's chest is surgically opened and an obstructed artery replaced with a native artery harvested elsewhere, has been the conventional treatment for coronary artery disease for the last thirty years. Such surgery creates significant trauma to the patient, requires long recuperation times, and causes a great deal of morbidity and mortality. In addition, experience has shown that the graft becomes obstructed with time, requiring further surgery.
More recently, catheter-based therapies such as percutaneous transluminal coronary angioplasty (PTCA) and atherectomy have been developed. In PTCA, a mechanical dilatation device is disposed across an obstruction in the patient's artery and then dilated to compress the plaque lining the artery to restore patency to the vessel. Atherectomy involves using an end effector, such as a mechanical cutting device (or laser) to cut (or ablate) a passage through the blockage. Such methods have drawbacks, however, ranging from re-blockage of dilated vessels with angioplasty to catastrophic rupture or dissection of the vessel during atherectomy. Moreover, these methods may only be used for that fraction of the patient population where the blockages are few and are easily accessible. Neither technique is suitable for the treatment of diffuse atherosclerosis.
A more recent technique, which holds promise of treating a larger percentage of the patient population, including those patients suffering from diffuse atherosclerosis, is referred to as transmyocardial revascularization (TMR). In this method, a series of channels are formed in the left ventricular wall of the heart. Typically, between 15 and 30 channels about 1 mm in diameter and up to 3.0 cm deep are formed with a laser in the wall of the left ventricle to perfuse the heart muscle with blood coming directly from the inside of the left ventricle, rather than traveling through the coronary arteries. Apparatus and methods have been proposed to create those channels both percutaneously and intraoperatively (i.e., with the chest opened).
U.S. Pat. No. 5,389,096 to Aita et al. describes a catheter-based laser apparatus for percutaneously forming channels extending from the endocardium into the myocardium. U.S. Pat. No. 5,380,316 to Aita et al. describes an intraoperative laser-based system for performing TMR. U.S. Pat. No. 5,591,159 to Taheri describes a mechanical apparatus for performing TMR involving a catheter having an end effector formed from a plurality of spring-loaded needles.
Neither the Aita nor Taheri devices describe apparatus wherein the laser-tip or spring-loaded needles are stabilized during the channel-forming process. Because the end effector of such devices may shift position while in use, such previously known devices may not provide the ability to reliably determine the depth of the channels, nor the relative positions between channels if multiple channels are formed.
In view of the shortcomings of previously known TMR devices, it would be desirable to provide apparatus and methods for performing percutaneous surgery, such as TMR, that permit precise control of the end region of the device carrying the end effector.
It also would be desirable to control the location of the end region of the device within the ventricle both with respect to features of the ventricular walls and in relation to other channels formed by the device, and to stabilize the end region of the device within the organ, for example, to counteract reaction forces created by the actuation of the end effector during treatment.
A number of devices are known in the medical arts that provide certain aspects of the desired functionality. For example, U.S. Pat. Nos. 5,389,073 and 5,330,466 to Imran describe steerable catheters; U.S. Pat. No. 5,415,166 to Imran describes a device for endocardial mapping; U.S. Pat. No. 4,813,930 to Elliott describes a radially extendable member for stabilizing an angioplasty catheter within a vessel; U.S. Pat. No. 5,354,310 describes an expandable wire mesh and graft for stabilizing an aneurysm; and U.S. Pat. Nos. 5,358,472 and 5,358,485 to Vance et al. describe atherectomy cutters that provide for aspiration of severed material.
None of the foregoing references overcomes problems associated with locating an end region of a catheter against a position on the inside wall of a heart chamber. Moreover, the prior art is devoid of a comprehensive solution to the above-noted shortcomings of previously-known apparatus for percutaneously performing surgery, and especially for performing TMR.